I wanted to make sure I understood exactly what you intended for this question. The East coast covers a lot of ground, and the people who live(d) along Lake Erie in western Pennsylvania are a couple steps removed from the "east coast" proper. Also "before, during, and after" is incredibly broad as well. I'll be back later with some information about the Erie Nation for you, since they're the ones who lived "specifically around the lakes in Pennsylvania", at least until the mid-1600s, unless you were looking for something else.

EDIT:

As far as we know, no European ever visited an Erie village while it was inhabited. The French knew learned of the Erie through Wendat (Huron) and Haudenosaunee (Iroquois) informants. Its from the Wendat that we get the name Erie, originally Eirehronon, which the French usually translated as "Cat Nation" but probably means "Raccoon Nation" though I know of at least one current researcher on the topic that prefers "Lynx Nation." The Erie were an Iroquoian people described by the Wendat as being very much like themselves.

One of the earliest French references to the Erie mentions that they had been pushed inland by their enemies to the west. This seems to have been a misunderstanding on the part of the French which, when combined to some other historical accounts, has caused all manner of confusion when determining exactly how large a territory the Erie actually controlled.

While some historians (even into the 20th Century) have ascribed an immense territory to the Erie, stretching along the coast of lake Erie from Buffalo, NY, to Toledo, OH, with a southern arm reaching down to Pittsburgh, PA. This hasn't panned out archaeologically, however, and the Erie-homeland itself seems to have been confined to the lake coast around Erie, PA, and Buffalo, NY. Archaeological settlements attributed to the the Erie are almost always found on the lakeshore or the rivers and streams, with the land inland seemingly to be reserved for hunting rather than settlement. In Pre-Contact times, the Erie seemed to have reached up further north toward the Oak Orchard Swamp just south of Lake Ontario, but were heading south as the Wenro (the easternmost members of the Neutral Confederacy) started moving into the region from the west. This is probably what the French were referring to in their early accounts of the Erie.

Based on how Erie towns were clustered, it has been suggested that they might have been a confederacy of at least three separate nations, much like the four nations of the Wendat or the five (later six) nations of the Haudenosaunee. 19th Haudenosaunee historians seem to back this up, describing what we call the Erie as an alliance between the Squakihaw, the Kah-Khaws, and the Erie-proper. We know the names of a few Erie towns from historical sources, but with the exception of Kah-Khaw town of Kakouagoga (you might notice the similarities in the two names), we're not sure exactly to which subset of the Erie the other two towns, Rigue and Gentaienton, belong. Based on linguistic connects, Rigue might be the main town of the Erie-proper, but that's far from conclusive. These three might represent the principal towns of each of the constituent nations of the Erie confederacy, but would not have been their own towns, assuming a settlement pattern similar to the Wendat and the Haudenosaunee.

In the 1650s, the Erie seem to have harbored Wendat refugees fleeing from Haudenosaunee conquest of Wendake (or as the Haudenosaunee would have put it, the liberation of Wendake from French control). These Wendat refugees brought French firearms with them and instigated a new war with the Haudenosaunee. By 1653, the Erie were burning Seneca towns (the Seneca are the westernmost of the Haudenosaunee and had moved into old Erie territory when the Wenro moved out of that region in 1638 as they broke away from the Neutral Confederacy to join the Wendat). The timeline of the Erie-Haudenosaunee conflict from here is a bit confused. We know several major events, but not precisely when they occurred. What follows is thought to be the most likely sequence, but is by no means certain:

After the Seneca towns were burned, A delegation of 30 Erie ambassadors were sent to the Seneca to help negotiate peace. At the peace summit, a confrontation occurred, beginning with an Erie killing a Seneca and resulting in only five of the Erie ambassadors escaping with their lives. Not long afterward, an Onondaga (the central-most members of the Haudenosaunee) war party passed through Erie territory on their way home from Lake Huron and were attacked. Two of the Onondaga were captured and one was presented to the sister of one of the deceased Erie ambassadors. This was standard procedure in an Iroquoian society; if your relative was killed by an enemy, the proper response was to capture a member of the enemy and give him or her to the women of the deceased's clan to determine how justice should be carried out. Usually, the captive would be adopted as a surrogate for the deceased and the matter considered resolved. More rarely, the captive would be executed. Unfortunately for the Onondaga captive, the ambassador's sister opted for execution despite prior promises of adoption. Unfortunately for the Erie, the captive was Anenraes, a prominent and popular leader among the Onondaga. The Erie-Seneca conflict had now expanded into an Erie-Haudenosaunee conflict.

In the summer of 1654, four of the Five Nations of the Haudenosaunee convened a war council; the Mohawk don't seem to have attended, but joined the fight later, adding 700 men to the 1200 that the Onondaga were fielding (we don't know the numbers for the other nations). The campaign against the Erie in the early fall of 1654 was successful, but not complete. The Erie were regarded as a numerous and formidable opponent (French reports estimate that the Erie could be guaranteed to have 2000 fighting men of their own during the initial conflict), and in 1655 the Onondaga were requesting military aid from the French to assist their continued campaign against the Erie. Unfortunately, 1655 is also a blank spot on the historical map for this area, as the Jesuit Relation, our main historical source for the area, is missing for that year. The record picks up again with the Jesuit Relation of 1656, which shows the Erie-Haudenosaunee War still ongoing, but the tide was turning in the Haudenosaunee's favor. By the end of 1656, the Haudenosaunee were victorious and the Erie scattered. The Erie diaspora likely accounts for the far-flung reports of Erie as far west as modern Toledo and as far south as Pittsburgh that show up on maps occasionally. The latest surviving post-diaspora Erie settlement surrendered to the Haudenosaunee in 1680 in (West?) Virginia.

While the Erie-Haudenosaunee War in the 1650s was the last significant conflict between the two confederacies, it was not the first. Turning to Haudenosaunee historians who recorded the history of their confederacy in the 1800s, we find additional information about the Erie Confederacy and their origins.

According to these accounts, the Erie Confederacy were originally part of the Haudenosaunee Confederacy, and to be more specifically, they were part of the Seneca. As the Erie moved further west they became more independent and culturally distinct, eventually breaking away from the Haudenosaunee and forming a separate Confederacy. One of the two histories we have attributes to this break to an Erie-Haudenosaunee War, while the other history says this war happened for other reasons and the break happened later.

I'll start with the David Cusick version, since it is written earlier (1825) and is regarded by Barbara Alice Mann, my main source on this, as being the more accurate of the two, as the latter version blends several incidents which Cusick accounts for separately as one war. Anyhow, in Cusick's version, during the time of the ninth Adoraroh (the Adoraroh being the life-time appointed leader of the Haudenosaunee Grand Council), the Jigonsaseh (the Adoraroh's equivalent in the women's council) was from the western Seneca, or Erie-proper. She was attempting to negotiate a peace between the Haudenosaunee and the Missisuakas, hosting a Missisaukas peace delegation in her home when two Senecas killed a Missisaukas sachem. This was a serious breach of the cease-fire that persisted while the peace delegation was visiting. The Jigonsaseh turned to two men over to the visiting Missisaukas to be punished as the Missisaukas saw fit, and traveled to Onondaga, the Haudenosaunee capital to consult with the Grand Council over the matter.

What transpired at the Grand Council is not known, but seem appears to have returned home and immediately called upon the Erie war chief to begin forming an alliance of non-Haudenosaunee peoples against the rest of the Haudenosaunee. Perhaps the Grand Council was poisoned against the Jigonsaseh by reports that came to them from a rival of the Jigonsaseh (and likely the woman who would become the new Jigonsaseh if the current one were deposed). Regardless the current Jigonsaseh and her alliance fought the Haudenosaunee to a draw and peace was restored. In Mann's analysis of these events, she believes the conflict was over rival interpretations of the Great Law, the Haudenosaunee constitution, and what actions the Jigonsaseh were permitted to perform in her mandate to secure peace and limit the excesses of war.

In 1881, Elias Johnson wrote a different version of the Jigonsaseh's civil war with the Haudenosaunee. In his account, she sided with Missisaukas because the division between the Erie and the Seneca had become so wide and embittered that when an opportunity to strike presented itself, the Jigonsaseh was easily swayed. During the course of this conflict the future members of the Erie Confederacy were all pushed out of Huadenosaunee lands and the office of the Jigonsaseh temporarily disbanded. This combines four events that in Cusicks history are separate incidents: the Haudenosaunee-Missisaukas conflict; the Haudenosaunee conflict with all three members of the Erie Confederacy (in Cusick version the Erie at the time Missisaukas conflict were not yet subdivided); the establishment of the Erie Confederacy as separate nation (Cusick says the Grand Council recognized their independence on more peaceful terms); and the expulsion of the Erie Confederacy from Haudenosaunee territory. The one thing that Mann thinks Johnson got right over Cusick is the timing. Johnson places this conflict in the last 13th Century, while Cusick puts it about a century and a half earlier, probably too close to the founding of the Haudenosaunee Confederacy.